Angular-sideband signal-forming transmitter



Nov. 9, 1965 E. BARTON 3,217,105

ANGULAR-SIDEBAND SIGNAL-FORMING TRANSMITTER Filed Jan. 115, 1961 2Sheets-Sheet 1 Nov. 9, 1965 E. BARTON ANGULAR-SIDEBAND SIGNAL-FORMINGTRANSMITTER v2 Sheets-Sheet 2 Filed Jan. 13, 1961 United States Patent O3,217,105 ANGULAR-SDEBAND SlGNAL-FGRIVHNG TRANSMITTER Loy E. Barton,Princeton, Nd., assigner to Radio Corporation of America, a corporationof leiaware Filed gan. 13, 1961, Ser. No. 82,518 Claims. (Cl. 179-15)The present invention relates to amplitude-modulation (AM) signaltransmission systems, and more particularly to phase-shifted or angulardouble-sideband two-channel amplitude-modulation (AM) signaltransmission systems for radio broadcast and other communicationpurposes. A signal transmission system of this type provides twochannelor stereophonic information in the form of angular or phase-shifteddouble-sideband modulation on a single carrier-wave or RF signal, fortwo-channel or stereophonic reception, and compatible single-channel ormonophonic reception. One channel has double sidebands leading thecarrier wave or signal by a given angle and the other channel has doublesidebands laggin-g the carrier wave or signal by the same angle. The twomodulation signals are each on both upper and lower sidebands.

The two-channel or stereophonic program material or modulation, such astwo stereophonically-related A and B audio-frequency signals, or the sumand difference thereof,

(A+B) and (A-B), is applied to angular components of the single carrierwave and transmitted on the carrier-wave to receivers which translatethe phase-shifted or angular double-sideband AM modulation and derivethe A and B signals, for respective application to separate soundreproducing means, or for other uses.

A quadrature system for stereophonic AM broadcasting, ot thisangular-modulation type, has been proposed in which the linalphase-shifted sideband angles are :L45 from the carrier wave, or 90between stereo channels. However the quadrature system appears to havecertain disadvantages including harmonic distortion problems formonophonic reception and decoding problems for stereophonic reception.

An improved angular-modulation signal transmission system in which thetwo double sidebands respectively lead and lag a resultant formedcarrier wave or signal by the same given angle and less than i45 isdescribed in my copending application, Serial No. 809,025, now PatentNo. 3,102,167, for Phase-Shifted Double-Sideband Two- Channel AMCommunications System. This system provides for reception with reducedharmonic signal distortion and greater compatibility in conventional AMreceivers. In this system, the phase shift of the sidebands from theresultant carrier wave, or the angular relation of the sidebands to thecarrier wave, is reduced to *30 or less, and provides a higher degree ofcompatibility for both two-channel or stereophonic AM reception, andstandard or monophonic AM reception.

The signal-forming transmitter or exciter of the present invention isadapted for use in such an angular-sideband system for modulated signaltransmission, and includes means for generating or deriving the basiccarrier signal, and means for separating the basic carrier signal intotwo carrier signal components for two-channel modulation andtranslation. The components are each amplitude modulated by dilerentmodulating signals, generally at audio frequency. The latter may .bestereophonically related. Each carrier signal component thus is providedwith double sidebands, and means are included in circuit with eachchannel for shifting the phase of the modulated carrier components 30with respect to the phase of the basic carrier signal, thereby to shiftthe sidebands substantially 60 apart. Means are also included forcombining the carrier components to provide the single formed carriersignal having i-SO" phase-shifted double sidebands. This Carrier and thetwo double sidebands are applied to the output power amplifier forbroadcast transmission.

The formed angular double-sideband AM signal is thus a composite carrierwave or signal having definite phase or frequency modulation informationthereon for twochannel or stereophonic broadcast transmission. The phaseor frequency-modulation components must be faithfully translated oramplied and transmitted. Proper forming of the modulated RF carriersignal with phaseangle or frequency-modulation information, as well asamplitude-modulation, thereon is essential for undistorted reception andchannel separation.

It is therefore, an object of the present invention to provide animproved low-level signal-forming amplitudemodulation (AM) transmitteror exciter, for a composite RF carrier wave or signal havingphase-shifted or angular double sidebands, for two-channel orstereophonic signal transmission, which is effective to establish andmaintain desired phase relations and modulation depth in the formedsignal.

It is also an object of the present invention to provide an improvedamplitude-modulated (AM) signal transmitter or exciter which willfaithfully form and translate a composite RF carrier signal havingangular double-sideband amplitude modulation for broadcast stereophonicand like signal reception, without undesirable phase shift or amplitudedistortion and with a high degree of eiciency.

The percent modulation possible without appreciable distortion, in asystem of this type, is normally relatively low and less than 20%Therefore, it has been considered to be virtually impossible to obtain asignal output from a forming transmitter or exciter in a system of thistype which would have modulation and effectively utilize thecapabilities of available electronic equipment. This is due in part tothe vector form of the two angular carrier signal components and theresultant carrier signal with its excess carrier signal amplitude. Thisexcess carrier signal amplitude precludes the possibility of obtaining100% modulation without distortion.

It is, therefore, a still further object of this invention to provide animproved signal-forming amplitude-modulation (AM) transmitter or exciterfor an RF carrier wave or signal having phase-shifted or angular doublesidebands, for two-channel or stereophonic signal transmission, which iseifective to establish predetermined signal-component phase relationsand substantially 100% modulation in the formed signal, withoutexcessive phase or amplitude distortion.

In accordance with the invention, this is `accomplished by reducing theexcess amplitude of the in-phase resultant of two angular (60) carriersignal components to that required for 100% modulation, in an improvedforming transmitter or exciter system which provides simplified, directand economical means for obtaining a two-channel or stereodouble-sideband angular-modulated Signal. This improved system includesmeans for producing three carrier signals or signal components in threebranch circuits, the first and second of which signals or signalcomponents are symmetrically angularly related to the third. For examplethe first and second carrier signals may be angularly separated fromeach other by substantially 60, or i30 with respect to the third carriersignal.

The system further includes means for amplitude modulating the rst andsecond carrier signals or signal components, and means for combining thethree carrier signals to provide a single resultant angular-modulatedoutput carrier signal. The third carrier signal or component is causedto be in phase opposition with the resultant of the irst and secondcarrier signals, which resultant is in phase with the carrier signal andof excess amplitude. The amplitude of the third carrier signal is thenadjusted to reduce the excess amplitude and produce a resultantdifferential output modulated signal or carrier wave, to be transmittedor applied to a high power transmitter, which is thus adapted for 100%modulation.

The invention will be further understood from the following descriptionwhen considered in connection with the accompanying drawings, and itsscope is pointed out in the appended claims.

In the drawings, FIGURE 1 is a schematic circuit diagram of anamplitude-modulated (AM) signal transmitter for two-channel angulardouble-sideband signals provided with a low-level signal-formingtransmitter or exciter system embodying the invention, and

FIGURES 2 and 3 are graphs showing vector-diagram representations andcurves illustrating the operation and certain features of thesignal-forming transmitter or exciter system shown in FIGURE 1.

Referring to FIGURE 1 and the transmitter shown therein, a crystaloscillator stage V1 provides a crystalcontrolled basic RF signal orcarrier wave Co at a predetermined frequency as indicated in the graph5. In the present example, the oscillator stage includes an oscillatortube 6 having a grid circuit 7 with a frequency-control crystal 8, andan anode output circuit lead 9 between which and common or chassisground 10, for the system, the oscillator signal output is derived. Inthe present example the frequency of the crystal, and of the basiccarrier wave or signal C may be considered to be 1170 kc. and within thepresent AM broadcast band. 'lhe oscillator stage V1 represents anysuitable or conventional means for obtaining a stable carrier wave orsignal frequency, and is the basic carrier-wave source for the sys`l temshown.

The oscillator is coupled to a signal-forming circuit or amplifier whichincludes three substantially parallel stages V2, V3 and V4 comprising,respectively, three amplifier tubes 12, 13 and 14 connected as signaltranslating devices in three separate branch circuits or channels whichinclude respectively circuit leads 15, 16 and 17. Chassis or commonground for the system serves as the common return circuit element. Thesignal-forming amplifier stages V2 and V4 are, effectively, converter ormodulator stages, and in the present example the tubes 12 and 14 thereinare of the pentagrid converter type having respectively, groundedcathodes 20 and 21, first control grids 22 and 23, screen grids 24 and25, second control grids 26 and 27, suppressor grids 28 and 29, andoutput anodes 30 and 31.

The control grid 22, for the converter or modulator stage V2, is coupledthrough a capacitor 35 with the signal channel lead 15, therebyproviding a signal input circuit, in conjunction with the groundedcathode 20. Bias potential e is applied to the grid 22 through asuitable grid resistor 36. Likewise the control grid 23, for theconverter or modulator stage V4, is coupled through a capacitor 37 withthe signal channel or branch lead 17, thereby completing the inputcircuit for the stage V4, in conjunction with the grounded cathode 21.Bias potential e for the grid 23 is applied thereto through a suitablegrid resistor 38 similar to that for the grid 22.

The amplifier stage V3 of the signal-forming amplifier operates as astraight signal amplifier and thus may include any suitable amplifierdevice. As represented in the present example, the tube 13 lis of thepentode type having a control grid 40 connected directly with the signalchannel lead 16 and having a cathode 41 connected through a variablegain-control bias resistor 42 to system ground 1t). The screen grid 43,together with the screen grids 24 and 25, is connected with a source ofpositive operating potential with respect to common ground, representedby a D.C. supply lead 44. The anode of the tube 13 is indicated at 45,and the suppressor grid 46 is connected to the cathode as shown.

The output circuit 9-10 of the carrier wave source V1 is connected tothe tuned primary winding 47 of an RF coupling transformer T1 through acoupling capacitor 48. The winding is provided with a shunt tuningcapacitor 49 and is variably tunable, as indicated, to the oscillatorfrequency. The transformer is provided with a secondary Winding 50having end terminals 51 and 52 which provide instantaneous signalpotentials respectively opposite polarities with respect to anintermediate grounded terminal 53. The terminal 51 is connected directlywith the channel lead 16 and the terminal 52 is connected indirectlywith both channel leads 15 and 17. The terminal 52 is connected first tovoltage-divider means cornprising two series resistors 54 and 55connected between the terminal 52 and common ground and having anintermediate output terminal 56. The terminal 56 is connected through alead 57 with a branch circuit terminal 58 to which the branch circuitleads 15 and 17 are connected through respective phase-shift networks 59and 60. The phase-shift network 59 comprises a series resistor 61 andcapacitor 62 connected between the terminal 58 and common ground 10,with the branch-circuit lead 1S connected at a terminal 63 at thejunction of the resistor and the capacitor.

The phase-shift network 60 likewise comprises a series capacitor 65 andresistor 66 connected between the terminal 58 and common ground 10, withthe branch circuit lead 17 connected with a terminal 67 at the junctionof the resistor and capacitor. In the present example the resistors 61and 66 may be assumed to be 470 and 800 ohms, respectively, and thecapacitors 62 and 65 may be assumed to have values of 150 and 300microfarads, respectively.

The secondary Winding 50 of the transformer T1 is relatively tightlycoupled to the tuned primary winding and provides an output voltage atthe terminal 52 which is reduced by means of the voltage divider 54-55at the output terminal 56 and the branch-circuit terminal 58. The latterterminal is connected as described, to the input circuits and firstcontrol grids of the signal-forming modulator stages V2 and V4 throughthe phase-shifting networks 59 and 60. At the input circuit of the stageV2 the phaseshift network 59 provides a 30 or lagging phase angle fromthe carrier or oscillator signal output at the terminal 52 and of thetuned primary winding 47. Likewise, at the input circuit of the stage V4the phase-shift network 60 provides a +30 or leading phase angle fromthe carrier or oscillator signal output at the terminal 52 and of thetuned primary Winding 47. As a result of this simplifiedchannel-dividing or branching and phase-shift circuit, the V2 stagesignal output has a 30 lagging phase angle with respect to the generatedcarrier signal and the V4 stage has a +30 leading phase with respect tothe generated carrier signal.

As hereinbefore referred to, the forming-amplifier stages V2 and V4 areconverters or modulators and include, in the present example, pentagridamplifier tubes, each having two signal input grids. Thus thetwo-channel or stereophonic modulation signals may be applied to theinput grid 26 of the amplifier tube 12 and to the input grid 27 of theamplifier tube 14, that is, to the second control grid of each tube,through suitable two-channel or stereophonic modulation signal supplycircuits as now will be described.

The grid 26 for the modulator stage V2 is connected through an inputgrid-circuit lead 73 and a coupling capacitor 74 with the variableoutput terminal or contact 75 of a potentiometer resistor 76 which isconnected in one modulation-signal supply circuit 77 from any suitablesource of audio-frequency modulation (not shown). As indicated by thelegend, this may be considered to be a channel A modulation signal, withan instantaneous frequency of 1000 cycles.

The potentiometer device -76 represents any suitable gain-control meansfor adjusting the amplitude or signal level of the modulating signalwhich is applied to the modulator stage V2. Bias potential for the grid26 issupplied through a grid resistor 79 connected with a biassupplylead 80 negative with respect to ground. An R-F by-pass capacitor 81 isalso connected with the grid circuit 73 in shunt relation thereto asshown.

In a similar manner, the modulation-signal input grid 27 of themodulator stage V4 is connected through an input grid-circuit lead 83and a coupling capacitor 84 with a variable output terminal or contact85 of a potentiometer resistor 86 which is connected in the othermodulation signal supply circuit 87 from any suitable second signalsource of audio-frequency modulation (not shown). In the presentexample, this may be considered to be a channel B modulation signal atan instantaneous frequency of 500 cycles. The channel A and channel Bsignals may be stereophonically related.

The potentiometer device 85-86 represents any suitable gain-controlmeans for adjusting the amplitude or signal level of the modulatingsignal which is applied to the modulator stage V4. Bias potential forthe grid 27 is provided through a grid resistor 89 connected with thebias supply lead 80, and an R-F by-pass capacitor 90 is connectedbetween ground and the grid-circuit lead 83, similar to that providedfor the grid-circuit lead 73.

The signal-forming amplifier is provided with a common signal outputcoupling transformer T2 for all three branch circuits and the amplifieror modulator stages V2, V3 and V4 therein. For this purpose, the branchcircuit anode output leads '70 and 71 and a branch circuit output anodelead 92 for the amplifier tube 13 are connected in corrnnon to a signalinput terminal 93 of the primary winding 95 of the transformer which istuned to the carrier signal frequency by a shunt tuning capacitor 96.The low-potential terminal 97 of the primary winding is connected withthe positive anode-potential supply-circuit lead 44 as indicated,whereby the anode currents for the three branch circuit amplifiers, andthe tubes 12, 13 and 14 therein, flow through the primary winding 95.

The output signals from the three branch circuits at the output circuitleads 70, 71 and 92 vectorially add in the primary winding of the tunedoutput circuit 94 of the broadband transformer T2 as provided by theprimary winding 95 and the shunt capacitor 96. The resultant RF outputsignal is derived from the secondary winding 99 and applied to signaloutput terminals 1130-101 through a suitable linear buffer-amplifierstage V5 and a tuned output coupling transformer T3 therefor. In thepresent example, the linear amplifier includes an electronic screengridtube 103 having a signal input grid 104 coupled to the high potentialside of the secondary 99 through a coupling capacitor S, and having acathode 106 connected to common ground or chassis through a cathoderesistor 107, to complete the grid input circuit through the groundedend of the secondary winding 99. The bias circuit for the grid iscompleted through a grid resistor 10S. A variable capacitor 109,representing any suitable variable gain-control device for thebuffer-amplifier stage VS, is interposed in circuit between the grid 104and the secondary winding 99. The anode output circuit 110 for thebuffer-amplifier stage V5 is connected to a variably-tunable primarywinding 111 for the coupling transformer T3, and through a supply lead112 to a source of positive anode operating potential. The transformersecondary winding 113 is connected directly with the output terminals100 and 101 of the signal-forming transmitter or exciter. The formed RFsignal available at the terminals 1013-101 may be utilized for anysuitable purpose. In the present example, for a broadcast transmitter,it is applied to an output power amplifier 114 of any suitable typewhich is coupled to a suitable transmitting antenna 115 and earth ground116 as shown.

The operation of this system is such that the carrierwave source V1provides the crystal-controlled basic RF signal or carrier wave, CO, ata predetermined fixed frequency, such as ll70kc. as referred tohereinbefore. This output signal is applied to the signal-formingamplifier stages V2, V3 and V4 through the tuned transformer T1. Thesecondary terminal 52 of the transformer has a signal output on one sideof the ground tap or terminal 53, of a predetermined voltage which isreduced by the voltage divider means and applied through the terminal 58and the phase-shift networks 59 and 60 to the branch circuits 15-10 and17-10 and the modulator stages V2 and V4. Two separate channelcarrier-signal components, C1 and C2, are thus derived at the outputcircuits 70 and 71, the former lagging the basic carrier orcrystaloscillator output signal by substantially 30, and the latterleading the basic carrier or crystal-oscillator signal output bysubstantially 30, as represented in the graphs 120 and 121 shown onFGURE 1. The channel A modulated-signal output of the V2 stage appearsat the tuned transformer T2, having the carrier component C1 with itstWo-sidebands due to the channel A modulation. Similarly the modulatedsignal output of the V4 stage appears at the tuned transformer T2,having the carrier component C2 with its two sidebands due to thechannel B modulation. The channel A sidebands for the 1000 cyclemodulation of the carrier component C1, and the channel B sidebands forthe carrier component C2 modulated at 500 cycles are indicated.

The other end of the secondary winding 50, that is the terminal 51, isconnected to the grid 40 of the third branch-circuit amplifier stage V3,and the signal voltage at the terminal 51 thus has an approximately 180phase angle from that at the terminal 52, both with respect to systemground.

As noted, the output circuits of all three of the signal formingamplifier branches are connected to the common broad-tuned RF outputtransformer T2. As a result, the common carrier-frequency signals of allthree branches add vectorially to obtain a resultant carrier signal C atapproximately Zero phase angle with respect to the reference phase ofthe carrier-wave source at the transformer T1. However sideband outputcomponents only occur at the output circuits 70 and 71 from themodulators V2 and V4. Therefore they retain their phase and amplitudeidentity in the output of the three stages V2, V3 and V4 through thetransformer T2, as represented in the graph 122. T he signal output fromthe transformer T3 at the terminals 10G-101 thus becomes the formeddouble-sideband two-channel or stereo signal which may be applied to anyparticular utilization means, such as the input circuit of thetransmitting power amplier 114 for any degree of amplification to thetransmitting antenna 11S.

Referring now to the graphs shown in FIGURES 2 and 3, along with thecircuit of FIGURE l, the audio-frequency channel A and channel Bmodulation applied to the third grids 26 and 27 of the modulator orconverter tubes 12 and 14, respectively, in the signal formingamplifier, cannot produce 100% modulation of the RF signal output (C1and C2) of the modulator stages V2 and V4 without appreciabledistortion. Consequently when the signal output of the modulator stagesV2 and V4 are vectorially added at the output transformer T2 in thetuned primary circuit 94, as represented in FIGURE 2, the resultantcarrier signal, CR, will have excess carrier amplitude.

The signal phase input to the V3 amplifier stage is substantially fromthe phase of the resultant RF signal from the stages V2 and V4, due tothe circuit-connections with the tapped secondary winding 50 ashereinbefore described. This relation is shown in FIGURE 2 wherein thecarrier signal from the V3 stage, designated as C3, is substantially 180out of phase with the resultant carrier signal CR from the two carriercomponents C1 and C2. Means are provided for making slight adjustmentsin the phase relation of the two signals C1 and C2, and is representedin the present example by the variable capacitor 124 connected betweenthe common branch-circuit lead 57 and ground for the system, precedingthe phase shift networks 59 and 60.

The percent modulation available through the modulator stages V2 and V4without distortion may be considered to be a maximum of 20%, asindicated on the carrier components C1 and C2 in FIGURE 2. The resultantcarrier signal change in amplitude is indicated by the in-phase vector125. When this is applied to the resultant carrier signal CR, asindicated at 125a and 125b, the carrier signal amplitude varies as thesum of these variations or changes, as indicated, The excess carriersignal amplitude, with respect to the zero or reference line, is alsoindicated in FIGURE 2. The third branch signal from the terminal 51 asapplied to the amplifier V3 at the signal input grid 40 is substantiallyequal to the signal at the grids 22 and 23 as derived from the voltagedivider means 54-55. Through this circuit connection with the secondary50, the third signal output from the amplifier stage V3 is in reversephase to the resultant CR of the two carrier components C1 and C2derived through the modulators V2 and V4. The gain control means 42 forthe third branch signal amplifier V3 permits a signal output therefromof sufhcient amplitude to cancel the excess amplitude of the resultantof the V2 and V4 stage output carrier signals, that is, the resultantcarrier signal CR, to permit 100% modulation of the output signal fromthe output transformer T2.

The cancelled excess carrier signal amplitude is represented in FIGURE 3between a line 126 and the zero or reference line. The required carriersignal amplitude is indicated by the arrowed line 127 and the newcarrier signal C is indicated by the arrowed line 128. It will be seenthat the carrier amplitude variation resulting from the modulation, andas represented by the sine-wave lines 129 now provides for substantially100% modulation of the new carrier signal C. This is shown for the newcarrier C, by the wave form 129 between limits represented by the zeroor reference line and the dotted line 130.

To adjust the value of the bucking signal or carrierwave component fromthe third channel amplifier V3 of the signal-forming amplifier, apractical -limit of audio voltage for modulation is applied individuallyto the modulators V2 and V4 from the signal input circuits 77 and 87 forchannels A and B. When the modulators V2 and V4 are modulated equally,and the same audio-frequency signal is applied to each channel, theoutput signal from the modulator stages V2 and V4 will be the vector sumof the carrier and the sidebands. The gain of the third channel stage V3is increased to apply the bucking carrier signal C3 to the mixing.transformer T2 -until the depth of modulation at the transformer T2reaches the zero axis and the peaks of the modulation are equal todouble the carrier wave amplitude, as represented in the lower portionof the graph of FIGURE 3. This is a normal monophonic 100% modulatedenvelope that occurs when the signals to the A and B channels produceequal modulation land are of the same frequency, and in phase.

When different or stereophonically-related audio signals are suppliedthrough the channel modulation circuits 77 and 87, the formed outputsignal at the .terminals G-101 is a phase-:shifted or angulardouble-sideband two-channel amplitude-modulation signal on one carrierwave and substantially free of phase shifts due to modulation. Thesidebands `due to the channel A modulation will have substantially 30angle with respect to the carrier signal C and the sidebands due to thechannel B modulation have substantially a -{-'30 phase angle withrespect to the carrier ysignal C. In this case, the two channel A and Bsignals may be separated in a receiver for `stercophonic signal output,or for other uses.

By this system, substantially 100% modulation of a phase-shiftedangle-modulation two-channel or stereo RF signal may be attained withrelatively low-cost and simple circuitry. In the forming transmitter, itwill be `seen that means are provided for producing three carrier signalcomponents, C1, C2 and C3, the first and second of which aresymmetrically angularly related to the third.

The system involves the use of a basic carrier signal couplingtransformer or like coupling means having a grounded intermediateterminal between the ends of the inductive coupling element or secondaryWinding thereof, and the phase-shift networks are connected between oneterminal and each of the modulators while the bucking-signal amplifierstage is connected with the other terminal of the said inductivecoupling element, thereby, with simplified circuitry, to establish thephase relation between the resultant and `bucking carrier signals ors-ignal components.

The means for amplitude modulating .the first and second carrier signalcomponents, C1 and C2, is readily provided by relatively simple andstable pentagrid-converter or like modulator means. The means forcombining the three carrier signal components C1, C2 and C3, with thethird carrier signal component, C3, -in phase opposition with theresultant, CR, of the first and second carrier signal components, isattained through the common tuned primary winding of the outputtransformer T2. The linear buffer amplifier stage V5 serves to preventany interaction between the utilization means coupled to the outputcircuit at the terminals 10Q-101 and the signal-forming amplifier mixingcircuit 94. The use of the formed RF output signal for 'further poweramplification and broadcast transmission represents .a present effectiveuse for the Signal forming transmitter or exciter of the presentinvention. It may yalso be used directly as a signal source to teststereo receivers of the angular-modulation type.

Having described the invention, what is claimed is:

1. A signal-forming transmitter for use in angular-sideband systems formodulated signal transmission, comprising in combination, means forproducing three carrier signal components, the first and second `ofwhich are angularly related to the third, means for modulating the firstand second carrier signal components, and means for combining said threesignal components, the third signal component being of opposite phasewith the resultant of the first and second `signal components and of `anamplitude to reduce the resultant of the first and second signalcomponents to provide a composite carrier signal having arelatively-wide modulation range.

2. In a two-channel angular-sideband signal transmitter, means forproducing three carrier signals, the first and second of which aresubstantially symmetrically `angularly related to the third, means foramplitude modulating the first .and second carrier signals, and meansfor combining said three carrier signals, with the third carrier signalin phase opposition with the resultant of the first and second carriersignals to reduce the resultant of the first land second signalcomponents to provide a composite differential output carrier signaladapted for substantially full modulation depth.

3. A signal-forming transmitter for use in angular-sideband systems formodulated signal transmission, comprising in combination, means forproducing three carrier signal components the first and second of whichare substantially symmetrically angularly related t-o the third, meansfor amplitude modulating the first and second carrier signal componentswith two modulating signals, a common tuned signal -output circuit, andmeans for combining said three signal components in said output circuit,with the third signal component in phase opposition with the resultant`of the first and second signal components yand of an amplitude toreduce the resultant of the first and second signal components toproduce a differential output carrier signal adapted for substantially`full modulation depth.

4. A signal-forming transmitter for use in an angularsideband system formodulated signal transmission, comprising in combination, meansproviding a basic carrier signal source having an output circuitincluding a coupling winding having two end terminals and anintermediate tap connected to ground for said system, means providingfirst and second branch signal circuits connected jointly with oneterminal of said coupling winding, phase shift networks in said branchcircuits providing substantially equal phase shifts positively in onebr-anch circuit and negatively in the other branch circuit for derivingtwo signal components having a predetermined phase differential inresponse to an applied carrier signal from said source through saidwinding, modulator means coupled to each of said branch circuits havinga common output circuit wherein the carrier-signal components derivedfrom said branch circuits are added vectorially to provide a resultantcarrier signal, signal-translating means coupled between the otherterminal of said coupling winding and said common output circuit for themodulator means for applying to said output circuit a carrier signalcomponent substantially 180 out of phase with said resultant carriersignal and substantially equal to the excess amplitude of said resultantcarrier signal above that required for effective 100% modulation.

5. A signal-forming transmitter for use in an angularsideband system formodulated signal transmission, comprising in combination, meansproviding a basic carrier signal source having a tunable output circuitresponsive to the carrier-signal frequency and including a couplingwinding having two end terminals and an intermediate tap connected toground for said system, means providing rst and second branch signalcircuits connected jointly with one terminal of said coupling winding, aphase shift network in each of said branch circuits providingsubstantially 30 phase shift positively in one branch circuit andnegatively in the other branch circuit for 4deriving two signalcomponents with substantially 60 phase differential in response to anapplied carrier signal from said source through said winding, meansproviding a pair of modulator stages coupled one to each of said branchcircuits and having a common `output circuit tunable to the carriersignal frequency and wherein the carrier-signal components derived fromsaid branch circuits are added vectorially to provide a resultantcarrier signal, and means including a signal amplifier coupled betweenthe other terminal of said coupling winding and said tunable outputcircuit for the modulator stages for applying to said output circuit acarrier signal component substantially 180 out of phase with saidresultant carrier signal and substantially equal to the excess amplitudeof said resultant carrier signal above that required for effective 100%modulation.

6. A signal-forming transmitter for use in an angularsideband system fortwo-channel modulated signal transmission, comprising in combination,basic carrier-signal generating means having a tunable output circuitincluding a coupling winding having two terminals and an intermediatetap connected to ground for said system, means providing first andsecond branch signal circuits connected jointly with one of saidterminals, means in said last named connection for reducing signalvoltages applied to said branch circuits, a phase-shift network in eachof said branch circuits providing substantially equal phase shiftspositively in one branch circuit and negatively in the other branchcircuit for deriving two signal components with a predetermined phasedifferential in response to an applied carrier signal from said sourcethrough said winding, means providing a pair of modulator stages coupledone to each of said branch circuits and having a common output circuittunable to the carrier signal frequency and wherein the carrier signalcomponents derived from said branch circuits are added vectorially toprovide a Iresultant carrier signal, means for applying two-channelmodulating signals to said modulator stages for modulating the first andsecond carrier signal components in said first and second branchcircuits, and means including a signal amplifier coupled between theother terminal of said coupling winding and said tunable output circuitfor the modulator stages for applying to said output circuit a carriersignal component substantially 180 out of phase with said resultantcarner signal and substantially equal to the excess amplitude of saidresultant carrier signal required for effective modulation, thereby toprovide a resultant output carrier having an amplitude adapted forsubstantially full modulation.

'7. A signal-forming transmitter for use in an angularsideband systemfor modulated signal transmission, comprising in combination, a tunableoscillator providing a basic carrier signal source, a tunable outputtransformer therefor having a secondary winding with an intermediate tapconnected to ground for said system, means connected with the secondarywinding on opposite sides of said tap for producing therefrom threecarrier signal components from said basic carrier signal, said lastnamed means including first and second branch signal circuits connectedwith said secondary winding on one side of said tap for translating afirst and second of said three carrier signal components and a thirdbranch signal circuit connected with said secondary winding on theopposite side of said tap for translating a third of said three carriersignal components, the signal components applied to said first andsecond branch circuits thereby being substantially out of phase withsaid -third signal component, a phase-shift network i-n each vof saidfirst and second branch signal circuits providing positive phase shiftin one branch circuit and negative phase shift in the other branchcircuit thereby to provide two signal components having a predeterminedphase differential and substantially symmetrically angularly related tosaid third signal component in response to an applied carrier signalfrom said oscillator through said secondary winding, means providing apair of modulator stages coupled one to each of said iirst and secondbranch signal circuits and having a common 4output circuit tunable tothe carrier signal frequency, means connecting said third branch signalcircuit with said common output circuit for combining said three carriersignal components, with the third carrier signal component in phaseopposition with the resultant of the first and second carrier signalcomponents in said output circuit, thereby to effect a reduction in theresultant carrier signal amplitude for increased eifective modulationdepth, means for applying different modulating signals to said modulatorstages for differently modulating said first and second carrier signalcomponents in the first and second branch signal circuits, buffer linearsignal amplifier means, and signal utilization means coupled to saidoutput circuit through said amplifier means.

8. A signal-forming transmitter for angular-sideband modulated-signaltransmission, comprising in combination, signal generator means, outputtransformer means therefor having a winding with a grounded intermediatetap, rst and second branch signal circuits connected with said windingon one side of said tap and a third branch signal circuit connected withsaid winding on the opposite side :of said tap, whereby signalcomponents from said generator means applied to said first and secondbranch circuits are substantially 180 `out of phase with a signalcomponent from said generator means applied to said third branch signalcircuit, a phase-shift network in each of said first and second branchsignal circuits providing a positive phase shift in one branch circuitand a negative phase shift in the other branch circuit to provide twosignal components having a predetermined phase differential andangularly related to said third signal component, means providing a pairof modulator stages coupled one to each of said rst Iand second branchsignal circuits and having a common output circuit tunable to thecarrier signal frequency, means for combining said three carrier signalcomponents in said signal output circuit with the third carrier signalcomponent in phase opp-osition with the resultant of the first andsecond carrier signal components, thereby to provide a resultant outputcarrier signal of reduced amplitude for increased effective modulationdepth, and means for applying different modulating signals to saidmodulator stages for differently modulating said first and secondcarrier signal components in 1 1 the first and second branch signalcircuits at relatively low amplitudes.

9. A signal-forming transmitter for angular-sideband modulated-signaltransmission, comprising in combination, signal generator means, outputtransformer means therefor having a winding with a grounded intermediatetap, first and second branch signal circuits connected with said windingon one side of said tap, a third branch signal circuit connected withsaid winding on the opposite side of said tap, a phase-shift network ineach of said first and second branch signal circuits providingsubstantially a 30 positive phase shift in one branch circuit andsubstantially a 30 negative phase shift in the other branch circuitthereby to provide two signal components having a predeterminedsubstantially 60 phase differential and substantially symmetricallylangularly related to said third signal component, signal modulator meanscoupled to each of said first and second branch signal circuits having acommon output circuit tunable to the carrier signal frequency, means forcombining said three carrier signal components in said signal outputcircuit, with the third carrier signal component in phase opposite withthe resultant -of the first and second carrier signal components,thereby to provide a resultant output carrier signal of reducedamplitude for increased effective modulation depth, means for applyingdifferent modulating signals to said modulator means for differentlymodulating said first and second carrier signal components in the firstand second branch sign-al circuits at relatively low amplitudes, bufferlinear signal amplifier means, and signal utilization means coupled tosaid output circuit through said amplifier means.

10. A signal-forming transmitter for use in an angularsideband systemfor modulated signal transmission, comprising in combination, meansproviding a basic carrier signal source, a tunable carrier-signal outputtransformer therefor having a secondary Winding with an intermediate tapconnected to ground for said system, first and second branch signalcircuits connected with said secondary winding on one side :of said tap,a third branch signal circuit connnected with said secondary winding onthe opposite side of said tap, a phase shift network in each of saidfirst and second branch signal circuits, means providing a pair ofmodulator stages coupled one to each of said first and second branchsignal circuits and having a common output circuit tunable to thecarrier signal frequency, means for combining carrier signal componentsfrom said branch signal circuits in said common output circuit, onecarrier signal component from the third branch signal circuit being inphase opposition with the resultant of carrier signal components fromthe first and second branch signal circuits, signal utilization meanscoupled to said output circuit, means for applying different modulatingsignals to said modulator stages for differently modulating said firstand second carrier signal components in the first and second branchsignal circuits, buffer linear signal amplifier means, and signalutilization means coupled to said output circuit through said amplifiermeans.

References Cited by the Examiner UNITED STATES PATENTS 1,608,566 11/26Potter 179-15 1,666,158 4/28 Offel 179-15 1,854,247 4/32 Brand 179-152,611,036 9/52 Norgaard 179-15 3,007,005 10/61 Moore et al. 179-15 OTHERREFERENCES Electronic Circuits and Tubes, Cruft Electronics Staff, 1947;McGraw-Hill.

DAVID G. REDINBAUGH, Primary Examiner,

ROBERT H. ROSE, Examiner,

1. A SIGNAL-FORMING TRANSMITTER FOR USE IN ANGULAR-SIDEBAND SYSTEMS FOR MODULATED SIGNAL TRANSMISSION, COMPRISING IN COMBINATION, MEANS FOR PRODUCING THREE CARRIER SIGNAL COMPONENTS, THE FIRST AND SECOND OF WHICH ARE ANGULARLY RELATED TO THE THIRD, MEANS FOR MODULATING THE FIRST AND SECOND CARRIER SIGNAL COMPONENTS, AND MEANS FOR COMBINING SAID THREE SIGNAL COMPONENTS, THE THIRD SIGNAL COMPONENT BEING OF OPPOSITE PHASE WITH THE RESULTANT OF THE FIRST AND SECOND SIGNAL COMPONENTS AND OF AN AMPLITUDE TO REDUCE THE RESULTANT OF THE FIRST AND SECOND SIGNAL COMPONENTS TO PROVIDE A COMPOSITE CARRIER SIGNAL HAVING A RELATIVELY-WIDE MODULATION RANGE. 